In that vein... Don't EVER let your players catch you fudging. Heck, don't fudge period. However, if you do start massaging probability for your dice then never, ever admit to doing it. Never. No matter how unlikely it may be to get back to your player.
Once the players stop believing you're a neutral arbiter of fate, things go down-hill quick. Every fluke of the dice becomes you out to get them, and every massive success is only because you let it happen.
I agree completely with this. In addition, even the appearance of GM cheating can lead to player group anger. The most common way this happens is a GM using a GM screen to shield dice rolls from player eyes. I used a GM screen for 2 decades because it was how I learned to GM. I got away with it too because I had the players trust, but once my SR campaigns turned deadlier the use of screens led to tons of paranoia and suspicion about what was going on back there.
Cheating to help the players is nearly as bad too. It's kind of like using the hand of god aka deux ex machina. (Not to be confused with the 3rd edition SR rule) Hand of god is where you save the party with some outside force. For example, the player characters are losing a firefight with an Ares Firewatch team and some npc Shadowrunner team just happens to stumble upon it and saves the party. Anyway, cheating on rolls or using the hand of god to save the party just makes players see you as an inexperienced GM putting them into dangerous situations they shouldn't have been put into in the first place. (Unless they earned it with sheer stupidity)
Also, using a sceen in SR is kinda dumb anyway cause it really slows you down with the use of all those dice.
The downside to not using a screen is that players can figure out your npc stats, but it's just not worth it in my opinion due to the above reasons, and so I dropped the use of screens in any game I GM.
On a related subject, remember that it is always better to make the enemies too weak on accident than to accidentally make them too powerful. There's always another Shadowrun coming up to try to retool the game balance and challenge the players. And it's very easy to murder players while trying to challenge them in Shadowrun, so careful careful careful. Don't put yourself in the position of becoming a Killer GM, or a clumsy GM that cheats to save the party from his own creations.
Whilst I think you have some good points here, I'm going to disagree slightly, whether to use a screen is going to be dependent on the group, some expect them, others hate them and the same goes for GMs, personally I rarely bother with them except occasionally as somewhere to stick quick reference notes (or if I have one for a particular system so I can refer to whatever tables it comes with quickly).
I'll also disagree on hand of godding players, but it's a very minor disagreement: I think again, you *can* do it if you're very careful, and personally I'd say only do it if the whole thing turns into a party wipe: having the party wake up with shiny new cortex bombs implanted and a whole new set of orders can be a way of keeping a game going rather than having everyone regen, but you have to be *very* careful if you do, if the players start thinking you'll bail them out of any trouble they get themselves into, that will start to affect how they act. So you should only do it occasionally and only with good reason, but like anything else it can be another tool in your arsenal.
To the OP: I don't know if you have prior experience GMing other systems, I'm relatively inexperienced at Shadowrun myself and others have already given you some great advice so I can't add much but the things I'd add for a totally new GM are:
1) Know any particularly relevant rules in advance.
If the run's targets defenses are weak in the astral making that an obvious point of incursion then read the Astral Combat rules before the session, even if you can't remember them on the spot a basic familiarity will save a lot of time and effort. The same goes for a Matrix Run or one involving a paranormal critter you don't normally use or even rules that just don't come up that often (plan to gas your players? Look up how toxins work).
2)Remember Rule 0: What the GM says, goes.
Don't be afraid to put your foot down or tweak the rules if needed, sometimes the rules are vague or simply don't cover a situation, sometimes somebody finds a gamebreaking combination by accident (My favourite technique for that case is to say: " You can do that this once since the rules technically allow it, but please don't use it again": I don't like penalising players for creativity, but if something is obviously going to break the game or the party apart or make the game simply not fun, sometimes you just have to say no, so that's my compromise, it may not be the best but I've found it usually seems to make players happy since they get their awesome move that they wanted to try out come off and I get to keep my game from fragmenting.
3) Remember Rule -1: The players reserve the right not to play.
Given what I said above remember the role of a GM is to make sure *everybody* is having fun, not to win, not to outsmart the players. Don't play favourites, don't let one person hog the spotlight etc. If the game isn't fun, pretty shortly you won't have a group. Remember as a GM if you want to kill the PCs you can just drop a Thor Shot on them and go for lunch but don't expect anyone to come back so when you use GM power, use it responsibly and get feedback from your players.On the flip side don't be too permissive either, I've seen starter GMs allow things that should never be allowed due to power or fluff issues because they wanted people to have fun and it wrecks the game for everyone else. It's also important to make sure your expectations about the game match with your players: if you're trying to run a down and dirty, scrabbling for a living in the radioactive sludge of Chicago campaign and the players want a Pink Mohawk kick in the door, nuke the guards, grab the girl and run type campaign then discord will result if that isn't addressed which leads me onto...
Rule 4: NEVER try and address an out of game problem in game.
This more or less speaks for itself and may fall under the heading of blindingly obvious but it's a mistake people keep making.
Rule 5: GMs don't kill players, Players Kill Players.
This rule harks back to rule 3. Sure intel is faulty, or a second runner team working for someone else shows up and everything goes to hell in a handbasket but never write a story to kill the players. This isn't D&D and the afterlife doesn't have a revolving door installed for your convenience. Nothing kills a group mood faster than thinking a GM is trying to kill the party or that the players are being railroaded.
Rule 6: Don't be afraid to let the hammer fall
That said if the players *do* do something monumentally stupid like kicking down the door to Saeder-Krupp HQ, mooning Lofwyr whilst yelling "Harlequin's a flower sniffing slot" then hammer them flat. Actions have consequences and if they don't... well there goes that sense of threat that keeps things interesting for the players. Power is like sugar: a little bit is nice but too much will just make you sick.
Rule 7: Whenever possible maintain player agency.
Agency is a funny concept but the quick and simple definition runs along the lines of "The ability to make choices about your destiny". If the players feel they have a choice they'll feel a lot happier about where they end up than if they feel you forced them here. Even if that choice was illusory (for example you set it up so that dragon you need them to talk to is in whichever building they decide to go to).
Rule 8: Everything has a counter, but don't counter everything.
It's very tempting to shut down paths after the players have used them once rather than letting them keep trying the same old thing again and again, and indeed this is something you should do from time to time to keep the players on their toes but if you counter everything the players do then fun goes out the window.
Rule 9: Geek the mage first is food tactics but don't do it every time
back to rule -1 again: don't let a player feel picked on and definitely *never* actually pick on a player.
That's all I can think of for now, I may post again with more and I'm sure some of the better GMs here will point out holes in my rules but I hope something there helps even if some of my rules above are really subsets of other rules.
